1. Field of the Invention
This invention is directed to haptic devices for intraocular lenses that provide increased comfort and performance to a patient. In particular, the invention is directed to haptic devices and designs, that consider a two-ring configuration within which the lens optic is held, that enhance post-surgical ocular health by maintaining separation of the anterior and posterior capsule of the human eye and therefore permit circulation of the aqueous humor within the capsule. Specifically, the invention, along with its various iterations, is designed to provide refractive stability by mitigating the extent of capsular fibrosis, and, in certain instances, mitigate the onset of other post-surgical conditions, specifically Posterior Capsular Opacification, as well as posterior segment conditions such as Age Related Macular Degeneration and Retinal Detachment.
2. Description of the Background
An intraocular lens (IOL) is an implanted lens in the eye, usually replacing the existing crystalline lens because it has been clouded over by a cataract, or as a form of refractive surgery to change the eye's optical power. The whole device usually comprises a small plastic lens with plastic side struts, called haptics, to hold the lens in place within the capsular bag inside the eye. Haptics also form the means of attachment of lenses to other areas of the eye, including the anterior angle or sulcus, the iris, and the posterior chamber ciliary sulcus. IOLs were traditionally made of an inflexible material (e.g. PMMA) though this largely been superseded by the use of flexible materials. Most IOLs fitted today are fixed monofocal lenses matched to distance vision. However, other types are available, such as multifocal IOLs which provide the patient with multiple-focused vision at far and reading distance, toric IOLs to correct for astigmatisms, and adaptive IOLs which provide the patient with limited visual accommodation.
Intraocular lenses have been used since 1999 for correcting larger errors in myopic (near-sighted), hyperopic (far-sighted), and astigmatic eyes. This type of IOL is also called PIOL (phakic intraocular lens), and the crystalline lens is not removed. More commonly, aphakic IOLs (that is, not PIOLs) are now used for visual correction errors (especially substantial hyperopia), and implanted via Clear Lens Extraction and Replacement (CLEAR) surgery. During CLEAR, the crystalline lens is extracted and an IOL replaces it in a process that is very similar to cataract surgery: both involve lens replacement, local anesthesia, both last approximately 30 minutes, and both require making a small incision in the eye for lens insertion. Patients recover from CLEAR surgery 1-7 days after the operation. During this time, patients should avoid strenuous exercise or any activity that significantly raises blood pressure. Patients should also visit their ophthalmologists regularly for several months so as to monitor the IOL implants. CLEAR has a 90% success rate (risks include wound leakage, infection, inflammation, and astigmatism). CLEAR can only be performed on patients ages 40 and older. This is to ensure that eye growth, which disrupts IOL lenses, will not occur post-surgery.
Once implanted, IOL lenses have three major benefits. First, they are an alternative to LASIK, a form of eye surgery that may not work for people with serious vision problems. Second, effective IOL implants may eliminate the need for glasses or contact lenses post-surgery. Third, the though the cataract may return, in the form of anterior or posterior capsule opactification (which results from the proliferation of lens corticular material between the capsule and the replacement lens, this may be controlled by additional surgical procedures such as an Nd-YAG laser capsulotomy. The disadvantage is that the eye's ability to change focus (accommodate) may have been reduced or eliminated, depending on the kind of lens implanted.
While significant advances have been made in the optical quality of aphakic lenses, most lenses currently made have an overall optical thickness of one millimeter or greater at the center optical focal point (e.g. see U.S. Pat. No. 4,363,142). In the late 1990's, two patents were applied for and subsequently issued for lens optics significantly thinner than the afore-referenced lens patents (U.S. Pat. Nos. 6,096,077 and 6,224,628). Although improved, the extreme thinness of the lens manufactured in accordance with U.S. Pat. No. 6,096,077 caused some minor distortions of the optic once in the eye, while the lens manufactured in accordance with U.S. Pat. No. 6,224,628 was poured of molded silicone and did not provide the desired visual acuity.
Generally, the natural lens separates the aqueous humor from the vitreous body. The iris separates the region between the cornea or anterior of the eye and the lens into an anterior chamber and a posterior chamber. The lens itself is contained in a membrane known as the capsule or capsular sac. When the lens is removed from the eye, the capsule may also be removed (capsular extraction), or the anterior portion of the capsule may be removed with the lens leaving the posterior portion of the capsule intact (extracapsular extraction). In an intraocular implant, the artificial or prosthetic lens may be inserted in the anterior chamber, the posterior chamber, or the capsular sac. The artificial lenses are usually fixedly attached within the eye, either by stitching to the iris, or by some supporting means or arms attached to the lens; in all cases the fixation mechanisms are categorized as haptics.
Several intraocular lenses designed for implant in the anterior chamber feature haptics with feet which support the lens in order to avoid the need for clips or sutures to secure the lens to the iris. The lenses work; however, sizing the lens to fit the eye is critical to avoid complications. These lenses have been made in lengths from 11.5 mm to 14 mm in 0.5 mm increments, and the thickness of the feet was about 250 microns.
A variety of lenses has been developed that provides up to four point support for the lens. The support structures for these haptics are often linked to the lens body so that the support structure should not deflect freely of the lens body, and therefore be liable to irritate portions of the eye in contact with the support structure. A variety of shapes and geometries for the lens supporting elements, or haptics, has been disclosed and described (U.S. Pat. No. 4,254,510; U.S. Pat. No. 4,363,143; U.S. Pat. No. 4,480,340; U.S. Pat. No. 4,504,981; U.S. Pat. No. 4,536,895; U.S. Pat. No. 4,575,374; U.S. Pat. No. 4,581,033; U.S. Pat. No. 4,629,460; U.S. Pat. No. 4,676,792; U.S. Pat. No. 4,701,181; U.S. Pat. No. 4,778,464; U.S. Pat. No. 4,787,902; U.S. Pat. No. Re. 33,039; U.S. Pat. No. 4,872,876; U.S. Pat. No. 5,047,052; U.K. Patent No. 2,165,456).
Despite the advances, there remain problems with intraocular implants. For example, when an intraocular lens is inserted in the eye, an incision is made in the cornea or sclera. The incision may cause the cornea to vary in thickness, leading to an uneven surface which can cause astigmatism. The insertion of a rigid lens through the incision, even with compressible haptics, requires an incision large enough to accommodate the rigid lens (typically at least 6 mm), and carries with it the increased risk of complications, such as infection, laceration of the ocular tissues, and retinal detachment. Deformable intraocular lenses made from polymethylmethacrylate (e.g. “PMMA”), polysulfone, silicone or hydrogel may be inserted through a smaller incision. Current science and advances in surgical techniques enables incisions of less than 2 mm (micro-incision) which may prove eventually to be beneficial to the patient, though any incision of less than 3.5 mm does not require sutures.
It is preferred that the intraocular lens be capable of insertion through a small incision. U.S. Pat. No. 4,451,938 shows an intraocular lens in which the lens body is made in two pieces so that each piece may be inserted through the incision separately and then joined by dowels after insertion in the eye. U.S. Pat. No. 4,769,035 discloses a foldable lens which may be inserted through an incision about 3.5 mm in length.
When the intraocular lens is inserted in the anterior chamber of the eye, the feet of the haptics, or lens supporting elements, generally lodge in the scleral sulcus, a depression anterior to the scleral spur where the iris and the ciliary muscle join the sclera in the angle of the anterior chamber. The scleral sulcus is crossed by trabecular tissue in which are located the spaces of Fontana. The anterior chamber of the eye is filled with the aqueous humor, a fluid secreted by the ciliary process, passing from the posterior chamber to the anterior chamber through the pupil, and from the angle of the anterior chamber it passes into the spaces of Fontana to the pectinate villi through which it is filtered into the venous canal of Schlemm. The lens should be positioned so the flow of fluid through the trabecular tissue is not blocked or glaucoma may result.
Since the feet of the haptics of anterior chamber lenses rest in the scleral sulcus, the flow of fluid is blocked where the feet are in contact with the trabecular tissue. It is therefore desirable to decrease the amount of surface area of the haptic foot in contact with the trabecular tissue. At the same time, the haptic feet have sufficient height to prevent adhesive tissue or synechia from growing around the feet and anchoring them to the iris or cornea. The opening of the trabecula is about 200 microns, and the haptic feet of conventional intraocular lenses are usually on the order of 175 to 200 microns, effectively blocking the openings in the trabecula wherever the feet are in contact with the tissue.
Other lenses that are situated in the posterior chamber may attach to the ciliary sulcus or be positioned in the equator of the capsular sac. In haptics with attachment to the ciliary sulcus, appropriate dimensioning is essential to ensure proper anchoring. In haptics with attachment to the capsular equator, recent science demonstrates the need for appropriate dimensioning also, as the haptic must place the lens properly in the capsule. If the haptic is too short for the capsule, the lens can dislodge or rotate in the eye, events that can require additional surgery to correct and can also cause intraocular trauma. Additionally, haptics that are too short for the capsule do not allow the lens to provide the patient with any desired or designed focal flexibility (that is, accommodation). If the haptic is too long for the capsule, the lens can angle either posteriorly or anteriorly at a greater angle than designed, in the former case significantly reducing visual acuity at distance and risking reverse accommodation, in the latter case putting pressure on the iris and diminishing focal flexibility.
U.S. Pat. Nos. 5,258,025 and 5,480,428 describe a lens surrounded by a sheet-like “positioner” having projections called “supporting elements either at the four corners of or continuously around the positioner, the supporting elements being 0.3 mm long and 0.01 to 0.05 mm thick (7″a and 7″b of FIG. 3 of the '025 patent, 18 of the '428 patent). However, the lens is for implantation in the posterior chamber, the lens of the '428 actually having a length short enough to “float.” In addition, the sheet-like nature of the positioner prevents independent deflection of the feet in response to forces applied by the eye.
In addition, the lens may place a greater or lesser degree of force on the haptic feet as the lens is compressed, depending upon construction of the lens. Since the amount of pressure for a given surface area is proportional to the force, it is desirable to decrease or distribute the amount of force placed on the haptic feet in order to diminish the force applied by the feet on the trabecular tissue. This goal is achieved by mounting the haptic arms on the ends of a flexible support bar in cantilever fashion, the support bar being offset from the lens body by a stem.
The act of surgically removing the natural lens and replacing it with an intraocular lens of whatever design gives rise to certain other possible conditions that can have a profound impact on the patient's ability to see clearly over a protracted period of time, the extent of focal accommodation that can be provided to the patient, and the effective positioning of the replacement lens in the eye. These conditions normally occur in a majority of cases but may be able to be mitigated with inventive lens and haptic designs. In particular, ophthalmologists have observed that the lens capsule will tend to atrophy over time. This is in part attributable to the fact that the replacement lens rarely occupies the entire lens capsule, and most lenses tend to flatten out the capsule, thus allowing the anterior and posterior surfaces of the capsule to adhere together, causing capsular fibrosis, atrophy, hardening, and adhesions. All these will necessarily diminish the effectiveness of any lens claiming to offer focal accommodation. In addition, it is possible that such fibrosis will cause the intraocular lens to re-position, either anteriorly or posteriorly, tilt, or decenter, any of which could cause significant change in the patient's refractive correction and quality of vision. It is possible that increased circulation of the aqueous humor can preserve the suppleness of the natural lens capsule, and preventing contact between the capsular surfaces should prevent capsular fibrosis, thereby protecting the integrity of the patient's refractive correction and overall visual acuity.
Some physicians have advocated the use of capsular tension rings to prevent capsular atrophy. However, these rings, which are situated in the lens equator, do not allow the ciliary body to influence the dimensions of the lens so as to provide for focal accommodation. Thus, whereas capsular retention rings may be effective when used in conjunction with non-accommodating or multifocal lenses, their value with premium lenses that claim accommodation is questionable.
In some cases post surgical adhesions can occur between the lens capsule and the haptic of the intraocular replacement lens. If significant enough, these adhesions can diminish the focal accommodative functions of the lens.
Posterior Capsule Opacification (PCO) is a condition that occurs in approximately 50% of cataract patients within three years after surgery. PCO is caused by the natural migration of lens epithelial cells from the anterior lens capsule to the equator Once the epithelial cells reach the equator, the cells die off leaving proteins of lens corticular material that accumulate on the posterior capsular surface in the form of Elschnig's pearls or of Soemmering's Rings. These fibroblasts that adhere to the capsule can cause significant shrinkage, and clouding of the lens. If the PCO migrates to the optical area of the capsule, vision is significantly impaired. The occurrence of PCO can be mitigated surgically by means of Nd-YAG-Laser correction, which perforates the posterior capsule with a hole that opens the optical zone of the posterior capsule. However, Nd-YAG laser capsulotomy surgery also carries risks of post-surgical complications including possible prolapse of the vitreous into the capsule (which can precipitate retinal detachment), and, as such, should be avoided if possible.
In the case of the inventive haptic designs incorporated herein, the inventors believe that the onset of PCO may be delayed or eliminated altogether through the use of appropriate haptic design to deter epithelial cell migration. In particular, 1) a haptic design that keeps the capsule open and prevents contact between the anterior and posterior surfaces may assist in mitigating PCO onset by maintaining hydration of the capsule, 2) the quality of the cataract or CLEAR surgery can assist in retarding PCO through assiduous cleaning and polishing of the anterior capsule, 3) the positioning of certain retention rings against the anterior of the capsule may arrest the migration of epithelial cells which cannot release their proteins until and unless they reach the fornix (equator) of the capsule; research demonstrates that if lens epithelial cells are dislodged from the anterior capsule they do not reattach, and 5) the positioning of certain retention rings in the fornix or against the posterior capsule may act to retain any corticular protein blasts at the periphery of the posterior capsule, and thereby prevent their aggregation in the posterior capsular optic zone. In some cases, IOL designers have found some success at mitigating the onset of PCO by configuring the posterior surface of the lens so as to provide a right angle at the junction of the lens with the posterior capsule. This configuration may be particularly applicable for those lenses that rest entirely against the posterior capsule and do not accommodate. In other cases, IOL designers have determined that the surface quality of the haptic may have some influence on PCO mitigation, though this topic continues to be debated. It is generally observed that absence of capsular fibrosis may also contribute to post-surgical capsular health and patient well-being.